Cyclic aromatic compounds have recently received attention, because of the characteristics derived from their cyclic structure, i.e., their structure-derived specificity. More specifically, the cyclic aromatic compounds have potential for development in applications of high-performance materials or functional materials and are expected to be used as inclusion compounds or to be used as effective monomers for syntheses of high molecular-weight linear polymers by ring-opening polymerization. Cyclic polyarylene sulfide (hereinafter polyarylene sulfide may be abbreviated as PAS) is a remarkable compound belonging to the category of cyclic aromatic compounds.
A proposed production method of cyclic polyarylene sulfide is, for example, a method of oxidative polymerization of a diaryl disulfide compound under an ultra dilute condition (for example, Patent Document 1). This method is expected to produce cyclic polyarylene sulfide at high selectivity and produce only a very low amount of linear polyarylene sulfide, and actually allows for production of cyclic polyarylene sulfide at a high yield. This method, however, requires the reaction under the ultra dilute condition and accordingly produces a very little amount of cyclic polyarylene sulfide per unit volume of a reaction vessel. This method accordingly has many problems in terms of producing cyclic polyarylene sulfide with high efficiency. This method has the reaction temperature of about room temperature and thus requires a long time of several ten hours for the reaction. This method accordingly has low productivity. Additionally, linear polyarylene sulfide produced as a byproduct by this method has low molecular weight including disulfide bond derived from diaryl disulfide as the raw material and low thermal stability and is practically not valuable. The linear polyarylene sulfide produced as the byproduct by this method has molecular weight similar to the molecular weight of the cyclic polyarylene sulfide as the objective substance, so that it is difficult to separate the cyclic polyarylene sulfide from the linear polyarylene sulfide as the byproduct. This method accordingly has extreme difficulty in production of high purity cyclic polyarylene sulfide with high efficiency. Additionally, this method requires an equal amount of an expensive oxidizing agent such as dichlorodicyanobenzoquinone to the amount of diaryl disulfide used as the raw material for the progress of oxidative polymerization. This method is thus not capable of producing cyclic polyarylene sulfide at a low cost. Another proposed method of oxidative polymerization of the diaryl disulfide compound under an ultra dilute condition performs oxidative polymerization in the presence of a metal catalyst and uses oxygen as the oxidizing agent. This method uses the inexpensive oxidizing agent but still has many problems, for example, difficulty in control of the reaction to produce a variety of and a large amount of oligomers and an extremely long time required for the reaction. In any case, the method of oxidative polymerization of the diaryl disulfide compound under the ultra dilute condition is not capable of producing high purity cyclic polyarylene sulfide at a low cost and with high efficiency.
Another proposed production method of cyclic polyarylene sulfide is a method of heating a copper salt of 4-bromothiophenol in quinoline under an ultra dilute condition. Like the above method of Patent Document 1, this method also requires the ultra dilute condition and a long time for the reaction and accordingly has extremely low productivity. Additionally this method has difficulty in separating copper bromide as a byproduct from cyclic polyarylene sulfide as an objective product and allows for production of only low purity cyclic polyarylene sulfide (for example, Patent Document 2).
A method disclosed to manufacture cyclic polyarylene sulfide at a high yield from general raw materials is a method of reacting a sulfidizing agent and a dihalogenated aromatic compound in 1.25 liters or more of an organic polar solvent relative to 1 mol of sulfur content in the sulfidizing agent (for example, Patent Document 3). This method, however, has only a low yield of cyclic polyarylene sulfide relative to the raw material monomer and produces a large amount of linear polyarylene sulfide as a byproduct. There is accordingly a need for improvement.
A method disclosed to produce cyclic polyarylene sulfide at a high yield is a method of exposing a dihalogenated aromatic compound such as 1,4-bis-(4′-bromophenylthio)benzene to sodium sulfide in N-methylpyrrolidone under reflux temperature (for example, Non-Patent Document 1). This method is expected to obtain cyclic polyarylene sulfide, since the volume of the organic polar solvent per 1 mol of sulfur content in the reaction mixture is 1.25 liters or more. This method, however, does not use linear polyarylene sulfide as the raw material and thus needs to use a large amount of a dihalogenated aromatic compound. This method also uses a very special compound as the dihalogenated aromatic compound and is thus industrially of little practical use. There is accordingly a need for improvement.
A method disclosed to solve the above problems is a method of heating and reacting a linear polyarylene sulfide, a sulfidizing agent and a dihalogenated aromatic compound in 1.25 liters or more of an organic polar solvent relative to 1 mol of sulfur content in the reaction mixture (for example, Patent Document 4). This method uses linear polyarylene sulfide as the raw material and thus reduces the amount of monomer used and improves the yield of cyclic polyarylene sulfide relative to the monomer. The method is accordingly expected to be industrially practical. This method has, however, been examined only for the procedure of simultaneously feeding and reacting all the reaction raw materials, i.e., linear polyarylene sulfide, a sulfidizing agent, a dihalogenated aromatic compound and an organic polar solvent. There have been no reviews for improvement of the yield and the formation rate of cyclic polyarylene sulfide and reduction of the impurity content by supplementary addition of the dihalogenated aromatic compound that is a preferred characteristic of the invention.
A disclosed multi-stage production method of cyclic polyarylene sulfide accompanied with supplementary addition of a dihalogenated aromatic compound is a method of performing a reaction (A) of heating a reaction mixture including linear polyarylene sulfide, a sulfidizing agent, an organic polar solvent and less than 0.9 mol of a dihalogenated aromatic compound relative to 1 mol of sulfur content in the sulfidizing agent and a reaction (B) of supplementary adding the dihalogenated aromatic compound and heating the reaction mixture in 1.25 liters or more of the organic polar solvent relative to 1 mol of sulfur content in the reaction mixture (for example, Patent Document 5). This method is characterized by cyclization of a low molecular-weight prepolymer obtained in the reaction (A) by supplementary addition of the dihalogenated aromatic compound in the reaction (B). In order to produce the prepolymer with high efficiency, it is preferable that substantially no dihalogenated aromatic compound is present in the reaction mixture in the reaction (A). Actually, only the method including no dihalogenated aromatic compound in the reaction (A) has been examined conventionally. In order to produce the prepolymer with high efficiency, it is also preferable that the volume of the organic polar solvent in the reaction mixture in the reaction (A) is less than 1.25 liters per 1 mol of sulfur content. Actually, only the method using 1 liter of the organic polar solvent in the reaction mixture per 1 mol of sulfur content has been examined conventionally. The effects on the yield have accordingly been unknown in manufacture of cyclic polyarylene sulfide in positive coexistence of a dihalogenated aromatic compound in the reaction mixture prior to supplementary addition of the dihalogenated aromatic compound under a diluter condition that the volume of the organic polar solvent is 1.25 liters or more per 1 mol of sulfur content through the entire reaction process.
The methods disclosed in Patent Documents 3 and 4 for recovery of cyclic polyarylene sulfide first recover a solid mixture mainly consisting of cyclic polyarylene sulfide and linear polyarylene sulfide by removal of part or most part of the organic polar solvent from a reaction mixture obtained by the reaction, subsequently expose the recovered solid mixture to a solvent that is capable of dissolving the cyclic polyarylene sulfide to prepare a solution including the cyclic polyarylene sulfide and remove the solvent used for dissolution from the solution, so as to obtain the cyclic polyarylene sulfide.
A method disclosed to produce high purity cyclic polyarylene sulfide similar to the above recovery method exposes a polyarylene sulfide mixture including at least linear polyarylene sulfide and cyclic polyarylene sulfide to a solvent that is capable of dissolving the cycling polyarylene sulfide to prepare a solution including the cyclic polyarylene sulfide and subsequently obtains the cyclic polyarylene sulfide from the solution (for example, Patent Document 6). These methods ensure production of high purity cyclic polyarylene sulfide. In order to produce the high purity cyclic polyarylene sulfide, however, the method requires the process of preparing a reaction mixture consisting of cyclic polyarylene sulfide, linear polyarylene sulfide and an organic polar solvent, the process of removing the organic polar solvent from the reaction mixture to produce a solid mixture including the cyclic polyarylene sulfide and the linear polyarylene sulfide, the process of exposing the solid mixture to a solvent to obtain a solution including the cyclic polyarylene sulfide and the process of removing the solvent from this solution. The procedure is thus rather troublesome.
A method disclosed to solve the above problems in recovery of cyclic polyarylene sulfide or more specifically to recover high purity cyclic polyarylene sulfide with high efficiency by a simple technique is a recovery method of cyclic polyarylene sulfide from a reaction mixture, which is characterized by removal of an organic polar solvent from a filtrate obtained by solid-liquid separation of the reaction mixture in a temperature range of not higher than the boiling point of the organic polar solvent under ordinary pressure, wherein the reaction mixture is obtained by exposure and reaction of at least a sulfidizing agent and a dihalogenated aromatic compound in the organic polar solvent and includes at least linear polyarylene sulfide and cyclic polyarylene sulfide (for example, Patent Document 7). Another disclosed method is a method of distilling out part of an organic polar solvent from a mixture including at least polyarylene sulfide, cyclic polyarylene sulfide and the organic polar solvent and subsequently recovering the cyclic polyarylene sulfide by solid-liquid separation (for example, Patent Document 8). These methods separate and recover cyclic polyarylene sulfide as the objective substance by the simple technique of solid-liquid separation. These are expected to improve the above problems of the prior arts. These methods, however, do not perform supplementary addition of a dihalogenated aromatic compound and further reaction, which are preferred characteristics of the invention, in the process of obtaining the reaction product including cyclic polyarylene sulfide. Accordingly, there is still a problem that a long separation time is required in the process of solid-liquid separation of the reaction product. Additionally, the resulting cyclic polyarylene sulfide has not sufficiently high purity. Further improvement is thus needed.